Weaver Ants

Sisterhood of Weavers

With a remarkable array of communication skills, weaver ants may have perfected social networking.

By Douglas H. Chadwick

Photograph by Mark W. Moffett

If aliens ever do land on Earth, don’t get all huffy if their greeting turns out to be: "Take me to your ant."

That ant might be a queen mother, weighing about the same as a few grains of salt. But she, along with other queens and their worldwide empires, would match the weight of the seven billion people seething across the planet these days. Plus, the queens and their offspring have been living in large, highly organized, cooperative societies—practicing activities from strategic army warfare to agriculture and livestock herding—for at least 50 million years. We've been at it for, what, 10,000, tops?

I'd nominate entomologist and photographer Mark Moffett as the aliens' escort. During years of jungle quests he has discovered new ant species and astonishing ant behaviors. Even over breakfast here in the rain forest of Queensland, Australia, he's pondering what sort of organism an ant colony amounts to, since it is this social group as a whole, not the individual, that really competes in the struggle for survival and evolves over time. Consider the colony as a unified body in which individual members are like cells, with castes of them performing separate duties like specialized organs.

Just above our heads, in the rain forest canopy, streams the almost perfect society. In other tropical and subtropical woodlands, scores of different ant species may share a single tree. But there's little room for coexistence where the ants known as Oecophylla make their home—one species here in Australia and in southern Asia, the other in parts of Africa. Long-legged and lithe, they so aggressively dominate huge territories in the forest canopies that locals simply call them the tree ants.

Or weaver ants, because they make their soccer-ball-size nests among the branches by sewing leaves together. Each weaver ant colony inhabits from half a dozen to more than a hundred nests at any given time, forming a metropolis of boroughs and suburbs connected by busy commuter routes. A hierarchy of workers and soldiers maintains and defends this territory, which spreads from treetops to the forest floor, staying in sync through constant communication. They touch each other with mouths, forelegs, or antennae. They lay down scents with different glands to send different messages. They release more pheromones into the air to broadcast signals quickly and widely. They even display symbolic behavior: To warn of an approaching enemy, for instance, they jerk their bodies in a kind of ritualized fight.

Scientists have likened weaver ant communication to a type of language with primitive syntax. Urban planners examine the organization of ant societies. Mathematicians draw upon analyses of ant behavior to devise parallel computing formulas (where multiple problems are solved simultaneously). Ants serve as models in all kinds of studies aimed at figuring out how big, complex jobs get done with small parts and a minimum of instructions.

Here is how a weaver ant nest-construction project gets under way.

A single worker stands on a leaf and reaches to grasp the edge of another leaf nearby. If the span is too great, a second worker climbs over the first, and the bottom ant grasps the newcomer by its wire-thin waist and holds it out closer to the goal. Still not enough? A third ant clambers over the first two and is lifted out farther yet. Ant by ant, a living chain grows into thin air like the arm of a construction crane. Once the distant leaf is grabbed, the squad pulls in unison, often with nest mates that have formed parallel chains and reinforcing cross-links, to draw the leaves' edges together. Workers begin to array themselves like live staples along the seam between the leaves, legs holding on to one edge, jaws gripping the other. And then? They wait.

As evening comes on and the humidity rises, more workers arrive from nearby nests. They're carrying larvae that are about to enter the pupal stage and metamorphose into adults.

Larvae of other ant species spin individual protective cocoons of silk. Oecophylla larvae donate their silk to the colony. Straddling the leaf seam, an adult uses its antennae to tap the head of the larva held in its jaws, telling it to extrude silk from its salivary glands. A worker's operating manual would read: Swing head to one side. Tappity-tap larva. Dab glob of its silk onto leaf. Swing head opposite way, drawing thread across to other leaf. Keep tappity-tapping larva. Dab next glob there. Step forward. Repeat procedure. When finished, move on to other tasks.